This paper examines nuclear energy output in a differential game framework involving two countries. The countries differ regarding nuclear technology with one being relatively safe and the other less safe. Simulation of a numerical model gives the following results, (i) A cooperative agreement will imply less use of nuclear energy compared with both a noncooperative Nash equilibrium and an uncontrolled market solution, (ii) The country with relatively safe nuclear energy technology benefits most from a cooperative solution, (iii) Starting from an uncontrolled market economy, an agreement between the countries to introduce taxation of nuclear energy will be beneficial for both countries. However, by starting from the noncooperative Nash equilibrium, an agreement to slightly increase the nuclear energy taxes will be most beneficial for the country with less safe nuclear energy technology.